Illaenus crassicauda is a species of trilobites belonging to the family Illaenidae. These trilobites lived in the middle Ordovician and in the Silurian age (443 - 418 million years ago). Fossils of this species have been found in the sediments of Sweden and Russia.Paleobiology DatabaseEuropeana.
Etymology The Latin species name crassicauda means "fat-tailed", with reference to the shape of the pygidium.
Description Illaenus crassicauda can reach a length of about . These trilobites are without glabella and without articulation of the tail. The cephalon has a high profile. The large bulbous head are distant from the axis of the head, close to the margin.Archive.org
References
V. Jaanusson Zur Fauna und zur Korrelation der Kalksteine mit Illaenus crassicauda (sog. Flagkalk) im Siljan-Gebiet Dalarnas Geologiska Föreningen i Stockholm Förhandlingar - Volume 69, Issue 1, 1947
External links Fossil ID